Modeling the imidization kinetics of AFR700B polyimide

Abstract AFR700B imidization was monitored using Fourier transform infrared spectroscopy (FTIR) by following the increase in the carbon‐nitrogen bond of imide groups displayed by the 1360 cm⁻¹ band over several isotherms. Imidization occurred until ∼300°C (572°F). This was confirmed by the presence of water up to 300°C (572°F) in thermogravimetric analysis‐mass spectroscopy (TGA‐MS) data. First, reaction kinetics were described by first‐order kinetics with a fast and slow region of reaction. However, this model did not accurately describe the data in the transition from the fast to the slow reaction region. Imidization is kinetically controlled at short times. However, when the monomers rapidly react to form a high molecular weight polymer gel, imidization is controlled by diffusion. Therefore, a second‐order kinetic/diffusion model was used to describe the imidiation kinetics. This resulted in a substantial improvement in the fit of the data. The kinetic/diffusion model can also be used to describe imidization in polyimides other than AFR700B.